ほく is for when it's used in combination with other kanji, like 北欧
But you have to keep in mind that this is for "country-specific characters" (or abbreviations) instead of full names. In 北米 (ほくべい) for example it would also be read as ほく, but not in 北朝鮮 (きたちょうせん) as the latter uses the full name (it just so happens that its full name is represented in kanji). So it's not that simple.
No, it's just that "Japan" isn't what the natives call the place.
That does make for a bad comparison with "America", admittedly, which the natives do call "America". We also call the UK "England". Sometimes.
The point is that the name of a place in another language is just the name of a place in another language. Just because it sounds like "English" shouldn't distract from its one possible meaning of the entire United Kingdom.
In japanese you pronounce the words exactly the same as the separate characters. Its not like in English where ph is pronounced "f". (VERY nearly) every time you see a character its going to be pronounced the same way whether its in a word or by itself. So just read the word as individual letters then say it faster.
This is more or less true when the kana are written normal size. But small kana change how the regular kana are pronounced.
This is a (relatively) complete list of all the kana and how they are pronounced. The only thing it does not cover is how
を are pronounced differently when they are used as grammatical particles ("wa" and "o" respectively). It also does not cover how small
つ affects the pronunciation. (It causes the next consonant to geminate.)
OrchidBlack, I can't comment directly to you because your comment is at the end of the line, but hopefully you get notified of this.
That's not entirely correct. イギリス is a borrowing from Portuguese (as Wiktionary may also tell you):
From Portuguese inglês (“English”, adjective)
Many of the centuries-old borrowings come from Portuguese, as they were ones of the first European sailors to reach Japan. This is also why, for example, "button" is ボタン in Japanese as it comes from the Portuguese botão.
"English" as borrowed from English is pronounced イングリッシュ instead.